1. Field of the Invention
The present invention relates to access to a Flash memory, and more particularly, to a method for managing a plurality of blocks of a Flash memory, and to an associated memory device and a controller thereof.
2. Description of the Prior Art
As technologies of Flash memories progress in recent years, many kinds of portable memory devices, such as memory cards respectively complying with SD/MMC, CF, MS, and XD standards, are widely implemented in various applications. Therefore, the control of access to Flash memories in these portable memory devices has become an important issue.
Taking NAND Flash memories as an example, they can mainly be divided into two types, i.e. Single Level Cell (SLC) Flash memories and Multiple Level Cell (MLC) Flash memories. Each transistor that is considered a memory cell in SLC Flash memories only has two charge levels that respectively represent a logical value 0 and a logical value 1. In addition, the storage capability of each transistor that is considered a memory cell in MLC Flash memories can be fully utilized. More specifically, the voltage for driving memory cells in the MLC Flash memories is typically higher than that in the SLC Flash memories, and different voltage levels can be applied to the memory cells in the MLC Flash memories in order to record information of two bits (e.g. binary values 00, 01, 11, or 10) in a transistor that is considered a memory cell. Theoretically, the storage density of the MLC Flash memories may reach twice the storage density of the SLC Flash memories, which is considered good news for NAND Flash memory manufacturers who encountered a bottleneck of NAND Flash technologies.
As MLC Flash memories are cheaper than SLC Flash memories, and are capable of providing higher capacity than SLC Flash memories while the space is limited, MLC Flash memories have been a main stream for implementation of most portable memory devices on the market. For example, according to the related art, user data will get lost at any time in a situation where the quality of a Flash memory degrades due to long-term use. More particularly, in contrast to the SLC Flash memories, the upper limit of the erase count of each block of the MLC Flash memories is relatively low, which causes the problem of the unstable characteristics to become unacceptable.
Please note that the upper limit of the erase count of each block of Flash memories typically decreases while a new process is utilized. Because of the progress of the process, Flash memory manufacturers may achieve the goal of reducing costs. In this situation, they would be more severely impacted by the unstable characteristics mentioned above. Thus, a novel method is required for enhancing the control of data access to Flash memories, in order to guarantee the completeness of user data.